Preliminary Remarks. 3 



but the parts are nevertheless pressed and crouded together ; and 

 if we examine those which surround the opening, caused by the 

 nail, we shall find sensible marks of this pressure. The nail in its 

 turn may likewise be pierced by steel, and this again by other 

 bodies. 



We hence infer that bodies, even the most hard and compact, 

 are not composed of matter absolutely continuous, but of parts 

 aggregated together, and placed at distances, which, under the 

 influence of external causes, may become greater or less. It 

 is on this account that the dimensions of any given mass of mat- 

 ter are capable of being increased by heat, or diminished by 

 cold, that the particles of salt admit of being separated and dis- 

 tributed, and as it were, lost among the particles of water ; that 

 mercury attaches itself to a piece of gold immersed in it, and in- 

 sinuates itself into the interior of this compact substance. These 

 mixtures and dissolutions sometimes take place without any ap- 

 parent augmentation of bulk, this bulk being estimated according 

 to the exterior surface of the bodies in question, without regard 

 being had to the void spaces, sensible or insensible to us, which 

 may be found to exist among their parts. In all this there is 

 only separation and mixture without any actual penetration of 

 material particles. 



This want of material continuity in bodies is known under 

 the general name of porosity, and we call pores the interstices or 

 empty spaces by which these particles are separated from each 

 other. Porosity seems to be a property common to all bodies, 

 although it does not belong to the essence of matter, since we can 

 conceive of sensible bodies which are entirely destitute of void 

 space. 



6. Thus admitting that bodies may be considered as com- 

 posed of smaller parts which constitute their essence, we may 

 be asked, what is the form and magnitude of these parts. As to 

 the magnitude, it should seem that if is extremely minute ; for 

 to whatever extent we carry the division, in the case of gold, 

 for example, by the processes of wire-drawing, filing, and beating, 

 the smallest particles preserve invariably all the properties that 

 belong to the entire mass. Crystallized bodies reduced to an 

 almost impalpable powder, upon being examined with a micro- 

 scope, are found to exhibit the same forms and the same angles 

 which characterize the whole mass of the crystal. We have 



